Hi, I had the same problem. Installer would almost complete, but backs up/rolls back and completely uninstall. It looked like when the file associations are being made in the registry, it some how had an error. Suspected that McAfee might be blocking the reassociations of extensions to paint.net (i have recently changed McAfee to be in high secure mode) and it turned out to be true. When i reinstalled after disabling McAfee access protections, it worked. Error seems to occur when a "access denied" condition occurs i guess. I hope this helps.
